2007B Known Features

For 2007B the following new feature has arisen and occurs intermittently in detectors #2 and #3:

There was some detailed engineering work on WFCAM during the first part of September in an attempt to fix the bright edge channel problem seen intermittently in previous semesters. Although the impact of this
has been substantially reduced a byproduct of this work is a new channel-level "offset" problem seen occassionally on detectors #2 and #3. An example of the effect is shown in this sky frame and occurs at about the 1% level of sky. It has not so far been seen in dark frames but occurs at all sky levels including twilight flats. The patterns are strongly, but not completely, anti-correlated between detectors #2 and #3
as can be seen in the example. They are also semi-regular in behavior which makes them hard to correct using conventional processing.